Chromium plated metal structures



United States Patent 3,249,409 CHROMIUM PLATED METAL STRUCTURES Henry G. McLeod, St. Catharines, Ontario, Canada, assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Filed Jan. 23, 1963, Ser. No. 253,271 3 Claims. (Cl. 29-199) This invention relates to improved chromium plated metal structures, and more particularly it relates to chromium plated metal structures having a greatly improved corrosion resistance and method for producing the same.

Metal structures such as iron, steel, zinc base die castings and the like are. customarily plated with a series of electrodepositions of copper, nickel and chromium. The

copper is electroplated as a smooth base coat, the nickel is electroplated over the copper plate for appearance and corrosion resistance and the chromium is plated over the nickel for decorative effect.

The corrosion resistance of such Cu-Ni-Cr composite electrodeposits is mediocre especially in northern indus- The objects of this invention may be accomplished by the electrodeposition of a thin layer of cadmium between the copper and nickel deposits of a composite CuNiCr electrodeposite on a metal substrate. This extra deposit functions as a barrier layer to arrest any corrosion that may have affected the top chromium and nickel layers. A marked improvement in corrosion resistance results from the presence of this barrier layer. The extent of this improvement is far greater than expected and far exceeds that due merely from the thickness of this deposit. Marked improvement has been obtained with barrier layers as thin as 0.1 mil.

The following example is given to illustrate the improved corrosion resistance of the barrier layers of this invention, it being understood that the details of these examples are not to be taken as limiting the invention.

Example Steel panels were plated with about 0.8 mil copper from a typical cyanide copper plating solution such as disclosed in Martin U.S. Patent No. 2,861,929 and then with about 0.7 mil nickel from a typical nickel plating solution such as disclosed in Towle U.S. Patent No. 2,972,571 and finally with about 0.01 mil chromium from a chromic acid plating bath, for example, as disclosed in Brown U.S. Patent No. 2,750,334. This represents a plating finish of the kind used commercially today.

Similar steel panels were next plated as in the preceding paragraph with copper, nickel and chromium with the exception that a 0.1 mil layer of cadmium was plated between the copper and nickel plates. The cadmium was plated from a typical cadmium plating bath such as disclosed in Hendricks U.S. Patent No. 2,085,747.

For comparison, panels were prepared in which the steel was plated with 0.1 and 0.5 mil cadmium followed by 3,249,409 Patented May 3, 1966 0.8 mil copper, 0.7 mil nickel and finally 0.01 mil chromium.

All panels were exposed to the Cass corrosion test with the results set forth below.

The Cass corrosion test refers to the copper accelerated acetic acid salt spray test developed for the auto industry to simulate corrosion observed on automobiles exposed to outdoor atmospheric conditions. This test is described in an article by W. L. Pinner in Plating, vol. 44, p. 763 (1957). Briefly, in this test, parts are exposed in a closed cabinet to a fine mist of salt solution containing 5% NaCl, 1 to 1.1. g. per gallon copper chloride (CuCl -2H O) and made acid to pH 3.2 with acetic acid. The temperature within the cabinet is maintained at 120 F. Parts are examined once a day and are rated according to the following tabulation.

No failure 5 Slight failure, not over 10% of total visible area affected 4 Moderate failure, 1030% of total visible area affected 3 Severe failure, 30%70% of total visible area affected" 2 Total failure, more than of total visible area affected 1 The term failure in the above tabulation refers to rust, cracks, pits and blisters.

The coated panels above-described when subjected to the Cass test had the following ratings:

Coating thickness, Mils Rating after exposure, hrs. Plating Order Cd Cu Cd Ni Cr 22 44 Clearly, the inclusion of a thin plate of Cd between Cu and Ni improved corrosion resistance markedly whereas a similar Cd plate between the steel substrate and the copper was substantially ineffective in the 44 hour test.

The cadmium barrier plates of this invention should have a thickness of at least 0.1 mil and may have as much thickness as desired.

Throughout the specification and claims, any reference to parts, proportions and percentages refers to parts, proportions and percentages by weight unless otherwise specified.

Since it is obvious that many changes and modifications can be made in the above-described details without departing from the nature and spirit of the invention, it is to be understood that the invention is not to be limited to said details except as set forth in the appended claims.

What is claimed is:

1. metal substrate having a protective corrosion resistant composite electroplate comprising an electroplate of copper, a barrier electroplate of cadmium, and successive electroplates of nickel and chromium.

2. A metal substrate having a protective corrosion resistant composite electroplate comprising an electroplate of copper, a barrier electroplate of at least 0.1 mil thickness of cadmium, and successive electroplates of nickel and chromium.

3 r 4' 3. A metal substrate having a protective corrosion re- FOREIGN PATENTS sistant composite electroplate comprising an electroplate 151 636 5/1953 Australia of copper, a barrier electroplate of cadmium and succes- 717:985 11/1954 Great Britain s1ve electroplates of nickel and chromlum.

5 OTHER REFERENCES References Clted'by the Exammer Handbook of Engineering Materials by Miner & Sea- UNITED STATES PATENTS stone, published by John Wiley & Sons, 1955., New York, 2,181,773 11/1939 Wernlund. Sections 2-331 2,388,019 10/1945 Strickland 29196.6 v 3 009 23 11 19 1 Wesley 204 XR 10 DAVID L. RECK,PrzmaryExamme1 3,045,334 7/1962 Berzins 29194 HYLAND BIZOT, Examiner. 

1. A METAL SUBSTRATE HAVING A PROTECTIVE CORROSION RESISTANT COMPOSITE ELECTROPLATE COMPRISING AN ELECTROPLATE OF COPPER, A BARRIER ELECTROPLATE OF CADMIUM, AND SUCCESSIVE ELECTROPLATES OF NICKEL AND CHROMIUM. 